The present invention relates to a non-linear position transducer for detecting the position of a valve controlling the rate of flow of air inducted to the cylinders of a heat engine, and particularly a butterfly valve controlled by an accelerator of this engine, conveniently one provided with an electronic injection system.
As is known, in such electronic injection systems for heat engines there is an electronic central processor which, in dependence on signals it receives from the various sensors, and via interpolation on memorised mappings, controls a plurality of injectors (in the case of multi-injector systems) or the individual injector (in the case of single injector systems), and also conveniently controls the ignition system.
To provide particular operating strategies of the electronic central control unit, signals from supplementary sensors, such as, for example, a sensor detecting the angular position of the butterfly valve, are provided to the central control unit, which signals can indicate the absolute angular value or a variation over successive instants. Usually a linear potentiometer is utilized as this position transducer which gives a sufficient guarantee of reliability and accuracy with a relatively low cost, this being coupled to a successive analogue-to-digital converter which supplies the signal to the central control unit.
In certain particular operating conditions, especially in transient conditions, and in the initial opening range of the valve, in which there is a wide variation in the rate of flow of air, the signal provided to the central control unit can have an insufficient resolution, limited by that of the analogue-to-digital converter, which is generally an eight bit device, and by the characteristics of the potentiometer, so that the operating sensitivity of the system can be inadequate in some cases.
Sometimes, therefore, potentiometers with non-linear characteristics have been adopted, (for example, logarithmic) or double ramp potentiometers, but these solutions are significantly more expensive and less accurate.